1. Field of the Invention
Embodiments of the invention generally relate to flow sensing with an array of pressure or strain sensors.
2. Description of the Related Art
A flowmeter consisting of an array of dynamic strain sensors mounted on the exterior of a pipe employs an array processing algorithm applied to signals from the sensors in order to estimate the velocity of pressure waves caused by acoustics in a fluid or turbulent eddies traveling with the fluid passing through the interior of the pipe. In application, time-series sensor signals are transformed to the frequency domain and a velocity reading is calculated by determining the time delay at which the coherence correlation of the sensors is maximized. Selecting a frequency range that includes the majority of the energy created by the pressure waves of interest but avoids spatial aliasing and rejects out-of-band noise can improve performance of the flowmeter.
These frequency limits may correspond to a reduced range of flow rates based on fluid density, such as 0.7 to 10.0 meters per second (m/s) if the expected fluids are liquids (water/oil) or 3.0 to 50.0 m/s if the fluid is mostly gas. However, this approach limits ability to achieve accurate performance over a wide dynamic range of flow velocities using a fixed-length sensor array, and requiring no manual adjustments as is desired. Further, a fixed frequency configuration may yield correct readings for only a very narrow range of flow rates or fail altogether in challenging conditions, such as gas at low flow rates combined with high acoustic noise levels caused by pumps or control valves, for example.
Therefore, there exists a need for an improved flow meter and methods of processing signals from sensors of the meter to determine output values.